Field of the Invention
The present invention relates to a toner for developing an electrostatic image (electrostatic latent image) to be used in image forming methods, such as electrophotography and electrostatic printing.
Description of the Related Art
In recent years, along with the development of computers and multimedia, a unit for outputting a full-color image on demand has been desired in a wide variety of fields ranging from an office to a house, and hence an improvement in performance of a copying machine or a printer has been required. Requirements for on-demand printing include an increase in capacity of a toner cartridge and a reduction in amount of toner to be used. In each of the cases, the lengthening of the lifetime of the toner cartridge is needed.
The following condition is required for lengthening the lifetime of the toner cartridge. The properties of the toner are not changed even by multi-sheet printing. In a related-art toner, inorganic fine particles are externally added to the surface of a toner base particle, and hence the inorganic fine particles enter a space between a toner particle and a photosensitive member to reduce a contact area therebetween. However, when the inorganic fine particles are detached by the multi-sheet printing, the toner base particle and the photosensitive member are liable to be brought into direct contact with each other. Accordingly, the contact area between the toner particle and the photosensitive member increases to deteriorate the transferability of the toner in some cases. In order to prevent such deterioration of the transferability, an investigation has been conducted on the suppression of the detachment of the inorganic fine particles not only through the external addition of the inorganic fine particles to the toner base particle but also through the application of heat or mechanical impact.
However, when the detachment of the inorganic fine particles from the toner base particle is suppressed, at the time of the application of a force to the inorganic fine particles, the force is liable to be transmitted as it is to the photosensitive member. Accordingly, an excessively large force is applied to the photosensitive member, and hence the surface layer of the photosensitive member is shaved at the time of the multi-sheet printing in some cases. Accordingly, when the inorganic fine particles are used, it has been difficult to achieve both an improvement in transferability of the toner and the prevention of the shaving of the photosensitive member at the time of the multi-sheet printing.
It is conceivable from the foregoing that when organic fine particles having hardnesses lower than those of the inorganic fine particles are brought into close contact with the surface layer of a toner base body, the shaving of the photosensitive member can be prevented. In, for example, Japanese Patent Application Laid-Open No. 2012-194314, there is a disclosure of a toner having protrusions formed of resin fine particles in the surface layer of a toner base body. In addition, in Japanese Patent Application Laid-Open No. 2015-106023, there is a disclosure of a toner in which after organic fine particles have been caused to adhere to the surface layer of a toner base body, the organic fine particles are fixed with a shell layer containing a thermosetting resin.
However, the transferability of the toner described in Japanese Patent Application Laid-Open No. 2012-194314 is low in some cases, though the stabilization of the chargeability of the toner and the heat-resistant storage stability thereof can be achieved by the resin fine particles. This is probably because the resin fine particles forming the protrusions have so low hardnesses as to be liable to deform, and hence a contact area between a toner particle and a photosensitive member increases. In addition, the toner fuses to a developing member in some cases. This is probably because the resin fine particles have so low hardnesses as to be liable to collapse, and hence the toner is liable to migrate to the developing member with the collapsed resin fine particles as starting points.
In addition, in the toner described in Japanese Patent Application Laid-Open No. 2015-106023, the detachment of the organic fine particles can be prevented by the shell containing the thermosetting resin, but as in the toner described in Japanese Patent Application Laid-Open No. 2012-194314, the transferability of the toner may be low or its fusion to a developing member may occur. A possible cause for the foregoing is as described below. The thermosetting resin is an organic shell layer and hence has a hardness lower than that of an inorganic shell layer formed of a silane coupling agent or the like. The resin fine particles are covered with the organic shell layer having a low hardness, and hence the deformation and collapse of the resin fine particles cannot be sufficiently prevented. As a result, the reduction in transferability or the fusion to the developing member may occur.
The present invention has been made in view of the problems. That is, an object of the present invention is to provide a toner that achieves both high transferability and the prevention of member contamination at the time of multi-sheet printing.